Collaborative Research: Midwest Low KV Collaboration: Continuation of Development of Low KV High Spatial Resolution EPMA Technique to Sub-micron Geological Features

该项目涉及开发使用电子探针显微分析仪的新技术，以扩展其在化学分析比以前可能的更小尺寸材料中的用途。该仪器通过将高能电子束聚焦在真空室内的目标样品上，然后测量该过程固有地产生的不同X射线。这项工作的基本原理是更好地了解物理过程-无论是在地质和地球材料，而且在人造材料在越来越小的尺度-与一个相对简单的仪器，可在许多大学，工业和政府的研究实验室。很多时候，材料中最小的特征可以提供有关材料如何创建的关键信息，以及人造材料如何断裂或失效的关键信息。在刚刚完成的NSF支持的项目（1554269）中，为了开发一种用于扩展较小电子束场发射电子探针显微分析仪的实用性的技术，我们在较低的加速电压下操作（即，7 kV）与传统的15-20 kV。在这些电压下，不会产生较高能量的K系列X射线线，例如过渡金属（例如Fe）的X射线线-需要测量和量化较低能量的L系列X射线。然而，使用这些L系列X射线存在一系列困难，因为它们由于光谱峰位移/形状变化而变得复杂，这是由相邻吸收边缘加剧的化学键合效应引起的，这增加了更多的复杂性。因此，单一或简单的参比标准品不再是有效的定量方法。在这个项目中，我们开发了一种创新的方法来处理这些铁的L-α X射线-铁是许多相关地质材料中的重要元素。这项研究的重点是含铁矿物橄榄石和铁硅化物（发现于陨石和月球表面）。这个新项目有几个组件来扩展这种技术：（1）将这一低kV Fe-L系列工作扩展到其他重要矿物，如硫化物、辉石、石榴石和角闪石，（2）扩展到研究某些含镍和富锰矿物的L线，（3）评估改进“等离子体”清洁样品测量的可能方法，（4）开发使用创新的软X射线发射光谱仪的协议，用于在低kV下产生的低能X射线，（5）探讨了利用DFT的可行性用密度泛函理论模拟了L系列过渡金属和M系列稀土元素的复杂光谱形状（其具有与Fe的L线等类似的一组条件），（6）研究高电子密度场发射束对样品的损伤。这项工作将在威斯康星大学麦迪逊分校和明尼苏达大学明尼阿波利斯分校的电子探针实验室之间进行联合合作。该项目将支持一名博士后研究员。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project involves development of new techniques in the use of the electron probe microanalyzer, to extend its usefulness in chemically analyzing smaller sized materials than previously possible. This instrument operates by focusing a beam of high energy electrons at a target sample inside a vacuum chamber, and then measuring the different X-rays inherently produced by this process. The rationale for this work is to better understand physical processes - both in geological and earth materials, but also in man-made materials at smaller and smaller scales - with a relatively simple instrument that is available in many universities, industrial and governmental research laboratories. Many times the very smallest features in a material can give critical information about how the material was created, and for manmade materials, how it will break or fail. In a just completed NSF-supported project (EAR-1554269), to develop a technique for extending the utility of the smaller electron beam field emission electron probe microanalyzer, we operated at lower accelerating voltage (i.e., 7 kV) vs traditional 15-20 kV. At these voltages, the higher energy K-series X-ray lines such those of the transition metals (e.g. Fe), are not generated - requiring that the lower energy L-series X-rays be measured and quantified. However, there are series difficulties with using these L-series X-rays, as they become complex entities due to spectral peak shift/shape changes, resulting from chemical bonding effects exacerbated by the adjacent absorption edge which adds more complexity. Thus, one single or simple reference standard is no longer a valid approach to quantification. In that project, we developed an innovative procedure to handle these iron L-alpha X-rays--and iron is an important element in many relevant geological materials. This research focused on the Fe-bearing mineral olivine and iron-silicides (found in meteorites and on the surface of the moon). This new project has several components to extend this technique: (1) extend this low kV Fe-L series work to other important important minerals such as sulfides, pyroxenes, garnets and amphiboles, (2) expand to look at L-lines of some Ni-bearing and Mn-rich minerals, (3) evaluate possible ways to improve measurements with "plasma" cleaning samples, (4) develop protocols using the innovative Soft X-ray Emission Spectrometer for the low energy X-rays generated at low kV, (5) investigate the feasibility of utilizing DFT (density functional theory) to simulate the complex spectral shapes of the L-series transition metals as well as the M-series of some rare earth elements (which have a similar set of conditions as the L-lines of Fe, etc.), and (6) investigate sample damage by the higher-electron-density field emission beam. This work will be done in a joint collaboration between the electron microprobe labs of the University of Wisconsin-Madison and the University of Minnesota-Minneapolis. The project will support a postdoctoral research fellow.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.